This invention relates to high pressure abrading processes and to coated abrasive products having particular utility for use therein.
For over half a century fused zirconium oxide (zirconia, or ZrO.sub.2) has been known to be a hard mineral having use as an abrasive grain for grinding wheels; see, e.g., U.S. Pat. No. 1,240,990. In this environment, fused zirconia has been used alone (U.S. Pat. Nos. 2,769,699 and 2,943,926) and also combined with fused aluminum oxide (alumina, or Al.sub.2 O.sub.3) either by blending grains of the two minerals (U.S. Pat. No. 3,175,894) or by forming grains from a hardened co-fused blend of alumina and zirconia (U.S. Pat. Nos. 1,240,990 and 3,181,939). Fused zirconia has also been employed as loose grain in polishing glass (see U.S. Pat. Nos. 2,624,661 and 2,955,031).
It is particularly interesting to note that apparently no one has heretofore contemplated the use of zirconia grains in a coated abrasive structure, for coated abrasive products are perhaps older than grinding wheels. Alumina grains and silicon grains are both, for example, commonly used in both molded wheels and coated abrasives. There are apparently sound reasons for not incorporating zirconia grains in a coated abrasive product, since zirconia is actually softer than garnet, an abrasive grain which is almost never employed in metal working. Even if a worker in the coated abrasive field had been sufficiently intrigued by zirconia to try it, he would have found that in most abrading operations performance was far below that achieved with the considerably less expensive aluminum oxide.
To show the normal effect of utilizing fused zirconia in coated abrasive products, two lots of materials were prepared. Each lot was made on a conventional starch- and glue-filled drills cloth backing, using conventional calcium carbonate-filled phenol-formaldehyde make and sandsize resins, and Grade 50 mineral. The sole difference between the two lots was the type of mineral employed--fused alumina for Lot A and Exolon "AZ-40" (co-fused 60:40 alumina: zirconia blend) for Lot B. Each lot was then slit to 3-inch width, formed into several 132-inch endless belts, and evaluated for ability to abrade various alloys. Each belt was in turn entrained over a smooth rubber contact roll driven at 6500 surface feet per minute, .+-. 5%. Compressed air was applied to a cylinder which urged the various workpieces against the belt, the total force actually applied being calculated from the line pressure and cylinder diameter. Initial rate of cut was then determined by 10 or 12 consecutive brief (3 to 5 second duration) grinding passes. Results are tabulated below:
__________________________________________________________________________ Test Total cut, Percentage piece Cross- Pressure on Total grind- grams cut material section workpiece, psi ing time, seconds Lot A Lot B Lot A Lot B __________________________________________________________________________ Waspalloy 3/4" diam. 10-20-30 36 23 8 100 35 circle 1095 tool " 340 30 205 137 100 67 steel Inconel " 575 30 253 148 100 58 Stainless steel 3/4" .times. 1/2" 400 30 158 95 100 60 1018 mild steel 1" .times. 1" 150-250-350 60 425 139 100 33 __________________________________________________________________________
It will be observed that on all five types of workpieces the initial rate of cut of coated abrasive products made with 60:40 co-fused alumina:zirconia abrasive grain is about one-third to two-thirds less than that of coated abrasive products made with fused alumina mineral.